Fix port conflict: use port 27018 for test MongoDB

Host machine already has MongoDB on 27017, so map the test
container to 27018 instead to avoid port allocation conflict.

.github/workflows/deploy.yml

@@ -23,7 +23,7 @@ jobs:
       mongodb:
         image: mongo:7
         ports:
-          - 27017:27017
+          - 27018:27017
         options: >-
           --health-cmd "mongosh --eval 'db.runCommand(\"ping\").ok'"
           --health-interval 10s
@@ -46,7 +46,7 @@ jobs:
       - name: Run tests
         run: npm test -- --runInBand
         env:
-          MONGO_URI: mongodb://localhost:27017
+          MONGO_URI: mongodb://localhost:27018
           JWT_SECRET: test-jwt-secret-for-ci
           NODE_ENV: test